From the Middle Miocene Temblor Formation of Central California

PaleoBios 29(1):13–23, June 22, 2009 © 2009 University of California Museum of Paleontology A new immigrant mustelid (Carnivora, Mammalia) from the middle Miocene Temblor Formation of central California zhiJie JaCk tseng1,2, XiaoMing Wang 2, J.D. steWart2 1integrative and evolutionary Biology Program, Department of Biological sciences, University of southern California, 3616 trousdale Parkway, Los angeles, Ca, USA 90089-0371; [email protected]. 2Department of Vertebrate Paleontology, natural history Museum of Los angeles County, 900 exposition Boulevard, Los angeles, Ca, USA 90007 a new mustelid genus from the Barstovian (middle Miocene) marine temblor Formation in California is described. the material of Legionarictis fortidens includes an incomplete cranium with partial upper dentition. the straight lingual border and slightly expanded posterointernal cingulum of M1 are plesiomorphic traits, as in the european Dehmictis. however, the M1 is not as posteriorly expanded, and the P4 does not have a lingual hypoconal crest, differentiating L. fortidens from younger north american forms. Furthermore, the P4 protocone is posteriorly placed from the parastyle crest, as in the extant south american Eira. an autapomorphic feature of L. fortidens is its highly hypertrophied P4 paracone with a bulbous crown. the robust upper carnassial, very strong development of the sagittal crest, and derived enamel microstructure all suggest a hard food component in its diet. the coastal depositional environment indicated by the presence of marine taxa in the temblor Formation suggests that hard shelled invertebrates might have been a food source of L. fortidens. a combination of plesiomorphic and derived dental characteristics puts the new form at an evolutionary stage basal to otters and closer to the living Eira. Cladistic analysis of craniodental characters suggests that L. fortidens is more derived than generalized basal mustelines of the old World, and may have diverged from the lutrine lineage in a separate immigration event to the new World. INTRODUCtion California Museum of Paleontology in Berkeley, California. Paleontological exploration in 1913 by the University of Comparative materials are housed at the natural history California Museum of Paleontology to the western edge Museum of Los angeles County, California and the american of the san Joaquin Valley in central California uncovered Museum of natural history, new York. Cladistic analysis was fossiliferous marine sandstone deposits of middle Miocene conducted using PaUP* (swofford 1993) with the heuristic age (Merriam 1914) (Fig. 1). the local fauna, subsequently search algorithm. all measurements were taken with a Mitutoyo named the “Merychippus zone”, contains both terrestrial and marine taxa (Merriam 1915). Collections by other institutions since then have produced additional large and small mammals (Bode 1935). in 2004, one of us (JDs) oversaw a paleontological mitigation project for the construction of a power transmission line near Monocline ridge north of Coalinga, and uncovered a new bone bed in the temblor Formation (kelly and stewart in press) (table 1). among the more than 1,200 vertebrate fossils collected from the new bone bed is a partial cranium of a new, unusual form: a large mustelid with very robust carnassial morphology and enamel micro- structural modification towards durophagy. Considering the proximity of the Merychippus zone fauna to the coast during the middle Miocene, this new mustelid might have consumed shelled invertebrates using its robust carnassials. the distinc- tive features of the new form warranted the naming of a new genus and species. its phylogenetic affinity lies in the middle Miocene diversification of basal mustelines. Furthermore, its basal position to the otters suggests that this new form probably split off from the lutrine lineage sometime in the early to middle Miocene, representing a distinct immigrant lineage from the old World. Figure 1. Map showing location of the Monocline ridge as- MATERIALs anD MethoDs semblage locality (UCMP V99563). topographic map modified the new material studied is housed in the University of from 1:24000 scale U.s. geological survey map. 14 PALEOBIOS, VOL. 29, NUMBER 1, JUNE 2009 vernier caliper to the nearest 0.1 mm. reconstructed illustration of the cranium was done using a traced outline of a photograph Table 1. a preliminary faunal list of the Monocline ridge as- of the specimen. examination of enamel microstructure was semblage (UCMP V99563). Modified from kelly and stewart done using a dissection light microscope. (in press). INSTITUTIONAL aBBreVIATIONS amphibia F:AM: Frick collection, american Museum of natural Anura, sp. undetermined history, new York, nY, USA eureptilia BM: British Museum, London, Uk Ophidia KUVP: University of kansas Museum of natural history, Colubridae Lawrence, KS, USA Masticophis or Coluber sp. LACM: natural history Museum of Los angeles County, Testudines Los angeles, Ca, USA Testudinidae LACM[M]: Mammalogy Collection, LaCM Hesperotestudo sp. of the H. osborniana-orthopyga NMNH: national Museum of natural history, Wash- lineage ington, DC, USA aves UCMP: University of California Museum of Paleontology, Anseriformes Berkeley, Ca, USA Anatidae UMMP: University of Michigan Museum of Paleontology, Branta cf. B. woolfendeni ann arbor, Mi, USA anatid, sp. undetermined Podicepidae sYSTEMATIC PaLeontoLogY Passeriformes, sp. undetermined class: mammalia Linnaeus 1758 Mammalia order: carnivora Bowdich 1821 Artiodactyla family: mustelidae Fischer de Waldheim 1817 Antilocapridae subfamily: mustelinae Fischer de Waldheim 1817 Cosorycinae, gen. and sp. indeterminate Legionarictis fortidens Camelidae (table 2, Figures 2–10) Miolabis sp. camelid, sp. undetermined Holotype—UCMP 166190, partial cranium with left i1-2, P2-4, right P2, and fragmentary left and right M1s. Carnivora Type locality—UCMP V99563 “Monocline ridge as- Felidae semblage,” 30 km north of the north Coalinga quarry near Pseudaelurus marshi Coalinga, California. the locality is on a small hill of the Mustelidae Monocline ridge between Panoche Creek and arroyo Cierro Legionarictis fortidens sp. et. gen. nov. (kelly and stewart in press). see table 1 for a preliminary Martes cf. M. glarea faunal list of the locality. Amphicyonidae Age and stratigraphy—UCMP V99563 is near the top Amphicyon ingens of the marine sandstone/pebble conglomerate temblor For- Canidae mation, which is overlain by the non-marine cross-bedded Microtomarctus conferta calcareous sandstone, mudstone, claystone, and pebble Borophaginae, sp. undetermined conglomeratic oro-Loma Formation (Bartow 1996). Based Lagomorpha on a study of perissodactyl and artiodactyl biochronology Leporidae, sp. undetermined (kelly and stewart in press), the locality is of early to early Perissodactyla late Barstovian north american Land Mammal age (middle Equidae Miocene) in age. Archaeohippus mourningi Etymology—Legionarius, a legionary soldier of the ro- Desmatippus avus man republic Period; ictis, weasel—generic name refers to “Merychippus” californicus the prominent sagittal crest of the holotype, reminiscent of “Merychippus” brevidontus the longitudinal helmet ornamentation of roman legionaries “Merychippus” cf. “M.” relictus and centurion officers. Fortis, strong; dens, tooth—specific Rhinocerotidae name refers to the robust carnassial of the holotype specimen. cf. Peraceras sp. Diagnosis—large mustelid, with very prominent sagittal Proboscidea, sp. undetermined crest similar to older individuals of the eurasian badger (Meles Rodentia, two undetermined. spp. Boddaert 1785); infraorbital foramina small, immediately TSENG et aL.—neW MUSTELiD FROM the MiDDLe MioCene teMBLor FM. oF Ca 15 above posterior root of P3 as in most basal mustelines; upper tooth formula 3/1/3/1/; i3 unenlarged, as in basal mustelines; P2-3 slender and simple, without accessory cusps; P4 protocone posteriorly offset from parastyle crest, slightly anterior in position to paracone, similar to Martes Frisch 1775; carnassial notch absent as in all neomustelids, P4 paracone very robust, labially and lingually inflated, invading the protocone space; P4 hypoconal crest absent as in basal mustelines; M1 triangular in occlusal view, with well-formed, straight lingual cingulum; posterior cingulum slightly expanded, M1 labial roots close together or fused, intermediate between the morphology observed in basal mustelines and lutrines. Description—Cranium: the entire cranium is dorsoventrally deformed; the compression is more severe on the right half in the ventrolateral direction (Figs. 2–5). associated with this asymmetrical deformation, much of the right upper dentition and zygomatic arch are destroyed. the nasal open- ing is dorsoventrally compressed to a width of 9.1 mm and a height of 4.0 mm; the nasal bones have been pressed into the nasal cavity, displacing the premaxilla and maxilla later- ally. the entire rostrum is 30 mm long between the anterior tip of the premaxilla and the anterior edge of the orbit. the antorbital fossa extends 11.5 mm anterior of the orbit. the infraorbital foramina are 2.4 mm wide and 3.34 mm high; they are situated ~11 mm dorsal of the posterior base of P3. Postorbital processes are not particularly prominent; two prominent frontal ridges lead from the postorbital processes and converge to form the sagittal crest ~8.4 mm posterior of the orbit. the sagittal crest rises gradually over the posterior cranium, reaching a maximum height of 14.0 mm; the crest measures 61.9

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